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| United States Patent |
5,107,091
|
|
Wagner
, et al.
|
April 21, 1992
|
Laser diode array mounting module
Abstract
A mounting module for a laser diode array has a microchannel heat sink
assembly and a circulation means for flowing a cooling fluid to and from
the microchannel heat sink so as to dissipate heat. The microchannel heat
sink has a plurality of internal microchannels, and has an external planar
surface to affix laser diode submounts which facilitate attachment of
laser emitting bars. The circulation mans comprises a housing having
canals which circulate the cooling fluid. The housing has an external
surface to which an electrical distribution means is placed, the
distribution means providing electrical power to the laser diode array.
| Inventors:
|
Wagner; David K. (South Pasadena, CA);
Danner; Allen D. (Pasadena, CA)
|
| Assignee:
|
Applied Solar Energy Corporation (City of Industry, CA)
|
| Appl. No.:
|
583170 |
| Filed:
|
September 14, 1990 |
| Current U.S. Class: |
219/121.84; 219/121.6; 219/121.76; 257/E33.075; 372/36 |
| Intern'l Class: |
B27K 026/00 |
| Field of Search: |
219/121.84,121.6,121.85,121.76
372/34,36
|
References Cited
U.S. Patent Documents
| 3872496 | Mar., 1975 | Potter | 357/81.
|
| 4727554 | Feb., 1988 | Watanabe | 372/36.
|
| 4758926 | Jul., 1988 | Herrell et al. | 361/385.
|
| 4881237 | Nov., 1989 | Donnelly | 372/34.
|
| 4894709 | Jan., 1990 | Phillips et al. | 357/82.
|
Primary Examiner: Albritton; C. L.
Attorney, Agent or Firm: Poms, Smith, Lande & Rose
Claims
We claim:
1. A mounting module for a laser diode array, comprising:
a plurality of laser emitting bars;
a planar microchannel heat sink assembly having a first and second surface,
a plurality of elongated submounts electrically connected in series, said
submounts attached to and connecting said laser emitting bars in series
and being connected to said first surface, said microchannel heat sink
assembly further including an intake vent and a plurality of exhaust vents
in said second surface and a multiplicity of microchannels running through
the interior of said heat sink assembly;
a manifold having a plurality of intake ports, a plurality of exhaust ports
and a plurality of internal canals, said intake and exhaust ports disposed
on an external surface of said module, said canals conducting said cooling
fluid from said intake port to said intake vent and from said exhaust
vents to said exhaust port; and
a power distribution circuit including a pair of electrical connection
points and a pair of electrical leads, each of said leads radiating from a
respective end of said elongated submounts electrically connected in
series to a respective one of said electrical connection points, said
electrical power distribution circuit enabling electrical power to flow to
said laser emitting bars via said submounts.
2. The module of claim 1, wherein:
said intake vent is elongated and bisects the width of said second surface,
and said exhaust vents are disposed parallel to said intake vent and
adjacent to opposite sides of said second surface.
3. The module of claim 1, wherein said cooling fluid is water.
4. The module of claim 1, wherein said cooling fluid is a mixture of water
and methanol.
5. The module of claim 1, wherein said electrical leads are of a metal
foil.
6. The module of claim 1, wherein said microchannels have a width of 50
micrometers.
7. The module of claim 1, further comprising:
a means for sensing the temperature of said microchannel heat sink, said
means comprising a thermocouple channel to measure heat from said
microchannel heat sink.
8. A laser diode array mounting module, comprising:
a housing having a manifold portion, an external portion and an emitting
surface, said manifold portion having a plurality of canals, said external
portion having a plurality of intake ports and a plurality of exhaust
ports;
a plurality of laser emitting bars electrically connected to a plurality of
submounts, said submounts being electrically connected in series and
affixed to said emitting surface, said plurality of submounts having a
pair of first electrical connection points, each of said first connection
points being disposed at a respective end of said serially connected
submounts;
means for distributing electrical power to said plurality of laser diode
submounts, said means having a pair of second electrical connection points
on said external portion of said housing, and a pair of electrical leads
radiating along the surface of said housing, said leads joining a
respective one of said first connection points with a respective one of
said second connection points;
a planar microchannel heat sink assembly having a first and second surface,
an intake vent, a plurality of exhaust vents, and a multiplicity of
channels which join said intake and exhaust vents and which are formed
interiorly of said heat sink assembly, said first surface providing said
emitting surface and said second surface being internal to said housing,
said intake and exhaust vents being disposed on said second surface, said
plurality of submounts being attached to said first surface by the use of
soldering;
said intake port attaches to one of said canals which further attaches to
said intake vent, and said exhaust vents attach to others of said canals
which join and further attach to said exhaust port, whereby, a path is
formed for the circulation of a cooling fluid throughout said module.
9. The module of claim 8, wherein said housing is constructed of plastic.
10. The module of claim 8, wherein said electrical leads are constructed of
a metal foil.
11. The module of claim 8, wherein said cooling fluid is water.
12. The module of claim 8, wherein said cooling fluid is a mixture of water
and methanol.
13. The module of claim 8, further comprising:
a means for sensing the temperature of said microchannel heat sink, said
sensing means comprising a thermocouple for measuring heat from said
microchannel heat sink.
14. The module of claim 8, wherein said microchannels have a width of 50
micrometers.
15. The module of claim 8, wherein said housing is constructed of ceramic.
Description
INTRODUCTION
Generally stated, the present invention relates to the mounting of solid
state circuitry and, more particularly, to a mounting module that provides
power to a laser diode array and further provides for cooling of the laser
diode array.
BACKGROUND OF THE INVENTION
Laser diodes are solid state electronic devices which convert electrical
power to light. Such devices are commonly used in applications requiring
high digital data rates, or electrical isolation of circuitry. The typical
device has a laser emitting bar formed of a solid state material which is
pumped or excited by pulsed electric current. The pumping of the device
causes photon energy to be emitted from the device. Frequently, a high
number of like devices are monolithically combined or stacked to form a
laser diode array.
A problem commonly encountered with laser diode arrays is the dissipation
of heat. A typical laser emitting bar operates at a range of 2 to 3 volts.
An array covering a surface of 1 cm.times.1 cm would typically contain 30
laser emitting bars and operate at a maximum of 90 volts. In ordinary
usage, the array would be pumped with electric current of up to 100 amps.
Assuming an average duty cycle of 1%, the total power to the array would
be 100 watts. Since the typical array converts roughly 30% of the power to
light energy, 70 watts of energy in the form of heat must be dissipated.
Without adequate cooling, at this power level the array would quickly burn
out.
In the prior art, numerous techniques have been suggested for cooling solid
state integrated circuits. One such technique, disclosed in U.S. Pat. No.
4,758,926, provides a microchannel heat sink having a plurality of
microscopic channels, or "microchannels." A cooling fluid is forced
through the channels, which draws away the waste heat. The solid state
device could be mounted directly onto the microchannel heat sink, or the
microchannel heat sink could be formed as a lower layer of the solid state
device.
A significant disadvantage and limitation of known microchannel heat sink
cooling techniques is that they are not readily adaptable to laser diode
arrays due to their significantly higher power and temperature dissipation
requirement over that of other solid state devices. Therefore, it would be
advantageous to provide a fully enclosed mounting module for a laser diode
array which utilizes microchannel heat sink cooling techniques. It would
also be desirable if such a mounting module could provide both power and a
cooling fluid to the laser diode array. Additionally, it would be
beneficial if the mounting module could be conveniently joined with other
like modules to form a larger matrix.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a
mounting module for a laser diode array. It is also an object of the
present invention to provide such a mounting module that can supply power
and cooling fluid to the array. It is yet another object of the present
invention to provide such a mounting module which could be combined with
other like modules to form a laser diode array matrix.
Generally stated, the present invention is directed to a mounting module
for a laser diode array. The module includes the provision of a manifold
portion which conducts power and cooling fluid to the array, and a
microchannel heat sink which provides structural support to the array and
dissipates heat from the array. The module can operate singularly or can
be combined with other like modules in a matrix.
More specifically, the mounting module of the present invention provides a
manifold portion having a plurality of canals for the routing of a cooling
fluid, and a microchannel heat sink having a multiplicity of internal
microchannels through which flows the cooling fluid. Additionally, the
microchannel heat sink provides a surface for attachment of laser emitting
bars and attachment points to provide a path for the conduction of
electrical power to the bars.
A more complete understanding of the laser diode array mounting module of
the present invention will be afforded to those skilled in the art, as
well as a realization of additional advantages and objects thereof, by a
consideration of the following detailed description of a preferred
exemplary embodiment. Reference will be made to the appended sheets of
drawings which will first be described briefly.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an exemplary laser diode array mounting
module of the present invention;
FIG. 2 is a partial view of the first surface of the exemplary microchannel
heat sink showing the laser diode submounts;
FIG. 3 is a partial view of the second surface of the exemplary
microchannel heat sink showing the input and output vents; and
FIG. 4 is a side view of an exemplary laser diode array mounting module
showing the exemplary circulation means; and
FIG. 5 is an exploded view of the exemplary microchannel sink, showing the
microchannels.
FIG. 6 is a side view of the exemplary submounts.
DETAILED DESCRIPTION OF A PREFERRED EXEMPLARY EMBODIMENT
Referring to FIGS. 1 and 4, a preferred exemplary embodiment of a laser
diode array mounting module in accordance with the present invention is
illustrated. The exemplary mounting module, shown generally at 10, has a
box shaped manifold portion 11 joined to a microchannel heat sink 30, as
will be described hereinbelow. It is intended that laser emitting bars 34
be affixed to the underside of the microchannel heat sink 30.
The exemplary manifold portion 11 is formed from a solid block of plastic,
ceramic or other suitable material, and may be, in one exemplary
embodiment, approximately 17 millimeters tall and 12 millimeters on the
side. It has a front panel 12a, a rear panel 12b, and a side panel 18. The
rear panel 12b is a mirror image of front panel 12a. The top of manifold
11 is generally triangular and formed from top panels 13, 14 and 15. A
circular input port 22a and output port 24a are diagonally disposed on
front panel 12a, with a similarly placed input port 22b and output port
24b on the rear panel 12b. Each of the input and output ports 22 and 24
are provided with O-ring seals 26 and 27. As commonly known in the
industry, the O-ring seals are used for connecting the ports externally,
such as to interconnect tubing. The input and output ports lead to a
plurality of canals internal to the manifold portion 11, as will be
described hereinbelow.
The microchannel heat sink 30 is rectangular in shape and provides a broad
surface area for the absorption of heat. In one exemplary embodiment, it
is approximately 1 millimeter in thickness and is exemplarily made of a
substrate material. As shown in FIGS. 2 and 3, the exemplary microchannel
heat sink has a first surface 31 for attachment of the laser emitting
bars, a second surface 32 which contacts the manifold portion 11, and a
means for attachment of laser emitting bars 34 to the first surface 31, as
will be described herein below.
The laser emitting bars 34 affix to the first surface 31 by the use of
submounts. The exemplary submounts are constructed from a three layer
sandwich of materials, consisting of a first layer of copper 90, a second
layer of aluminum oxide 91 and a third layer of tungsten copper. The
copper layer attaches to laser emitting bars 34 by use of known soldering
techniques including a foil contact 93, and the tungsten copper layer 92
adheres to the first surface 31, also by soldering techniques.
Accordingly, a thermal path is formed for conducting excess heat generated
by the laser emitting bars 34 first to the submounts, then into the
microchannel heat sink 30. The submounts also conduct electrical power
into the laser emitting bars 34.
The first surface 31 is dimensioned to accomodate exemplarily thirty laser
emitting bars 34 to be attached thereto per the technique described above.
The laser emitting bars 34 would be mounted in adjacent rows, or stacked.
Adjacent sides of the submounts are connected electrically, so that the
plurality of submounts are in series. At each end of the stack of serially
connected submounts 33 are metal spacers 47a and 47b. The spacers 47a and
47b electrically connect to submounts 33, as will be described
hereinbelow. It is anticipated that up to 90% of the surface area of the
first surface 31 be covered by laser emitting bars 34.
In an alternative embodiment of the present invention, a stack of laser
emitting bars 34 is attached to first surface 31 by use of a thin epoxy
joint. In yet another embodiment of the present invention the stack of
laser emitting bars 34 is coated with a thin insulator and metal film.
This coating forms the submount 33 directly onto the laser emitting bars
34, which is then soldered to first surface 31.
Referring now to FIG. 5, the exemplary microchannel heat sink 30 comprises
a manifold plate 35 and a channel plate 36. The manifold plate 35 provides
the second surface 32, and associated intake vent 37 and exhaust vents 38a
and 38b. The channel plate 36 has a multiplicity of alternating
microchannels 39 in its interior portion, and provides the hereinabove
described first surface 31. The channel plate 36 and manifold plate 35 are
attached together using known bonding techniques to form the microchannel
heat sink 30. Microchannel heat sinks of the type described can be
commonly found in the industry.
As shown in FIG. 3 the intake vent 37 bisects the width of the second
surface 32, and the exhaust vents 38a and 38b run parallel to the intake
vents and are adjacent to opposite edges of the second surface 32. The
plurality of vents lead to the multiplicity of microchannels 39 within the
microchannel heat sink 30, as exposed in FIG. 5. In an exemplary
embodiment, the microchannels would be approximately 50 micrometers in
width, and cross the breadth of the microchannel heat sink, following an
alternating path which leads from the intake vent 37 to each of the
exhaust vents 38a and 38b. The microchannels 39 guide the flow of a
cooling fluid through the microchannel heat sink 30, whereupon heat is
drawn away from the first surface 31 by the flowing fluid.
In the present invention, a circulation means is provided to route the
cooling fluid to the microchannel heat sink 30. The circulation means
flows the cooling fluid from an external source to the microchannel heat
sink intake vent 37, and then flows the cooling fluid from the
microchannel heat sink exhaust vents 38a and 38b to an external drain. The
exemplary circulation means comprises the intake ports 22a and 22b, the
exhaust ports 24a and 24b, and the plurality of canals internal to the
manifold portion 11.
As shown in FIG. 4, a horizontal intake canal 52 links the intake ports 22a
and 22b. A vertical intake canal 53 joins the center of horizontal intake
canal 52, and leads to the bottom of the manifold portion 11 to a location
adjoining intake vent 36. Similarly, a horizontal exhaust canal 54 links
the exhaust ports 24a and 24b, and a pair of vertical exhaust canals 55
and 56 join the horizontal exhaust canal 54, leading to the bottom of the
manifold portion 11 to locations adjoining exhaust vents 38a and 38b,
respectively. The network of canals allows for the cooling fluid to enter
an intake port 22 and flow through the intake canals 52 and 53 to the
intake vent 37. The canals can be easily formed in the solid plastic
manifold portion 11 by known machining techniques. After passing through
the microchannel heat sink 30, the cooling fluid flows from the exhaust
vents 38a and 38b through the exhaust canals 54, 55 and 56 to an exhaust
port 24.
To prevent leakage of cooling fluid from between the boundary adjoining the
manifold portion 11 and the microchannel heat sink 30, gasket 28 is
provided, which is inserted between the two components. The exemplary
gasket 28 has openings corresponding to the intake vent 37 and exhaust
vents 38a and 38b.
As described hereinabove, laser emitting bars draw a substantial amount of
power. Therefore, in the present invention, a means for distributing
electrical power to the bars 34, is provided. The exemplary electrical
distribution means, shown generally at 40, is formed of a metal foil, and
has a first connection pair 42a and 42b, an elongated portion 46a and 46b,
and a second connection pair 48a and 48b. The first connection pair 42a
and 42b are disposed on top panels 13 and 15 respectively, and provide
points for the input of electrical power. Exemplary screws 44a and 44b are
associated with the first connection pair 42a and 42b, and provide for the
attachment of an external power source, such as by wires. The elongated
portions 46a and 46b traverses the length of the manifold portion 11
within an associated groove 17a and 17b. The second connection pair 48a
and 48b electrically connects to metal spacers 47a and 47b, which
electrically connect to the outermost ones of the serially connected
submounts 33. Electrical power is therefore enabled to travel from an
external source to the submounts 33 and into the laser emitting bars 34.
Additionally, the metal foil of the electrical distribution means 40
provides structural integrity to the exemplary mounting module, in that it
holds the manifold portion 11 and the microchannel heat sink 30 together.
It is anticipated that the laser diode array mounting module of the present
invention be used either alone or linked into a network of like modules.
Operating singularly, one of the input ports 22 and one of the output
ports 24 would be blocked. By connecting a cooling fluid source to the
remaining input port 22, and a drain to the remaining output port 24,
fluid pressure would force a flow of cooling fluid through the manifold
portion 11 and microchannel heat sink 30, thereby cooling the device. In a
network mode, the second set of input and output ports, 22 and 24
respectively, would be connected to an adjacent, similar module. This way,
a single cooling source could be utilized to cool the entire network.
It is further anticipated that the mounting module of the present invention
be equipped with varying numbers of laser emitting bars, depending on the
desired usage of the operator. The operator can utilize different cooling
fluid mixtures depending on the density of the laser emitting bars and the
desired operating temperature. For usages requiring an operating
temperature of 40.degree. C., it is anticipated that water be used as the
cooling fluid. For usages requiring lower temperatures, such as below
0.degree. C., it is anticipated that a mixture of water and methanol be
utilized.
An alternative embodiment of the exemplary laser diode mounting module
further comprises a means for sensing the temperature of the microchannel
heat sink. The sensing means would enable the prevention of over heating
of the laser emitting bars, and any associated heat related damage to the
module. A thermocouple channel 57 would be provided in manifold 11, as
best shown in FIG. 4. Channel 57 is a port through which a thermocouple
wire may be inserted. The temperature of the microchannel heat sink 30 can
be measured at the thermocouple port 58 by known measuring techniques. For
example, the thermocouple would be inserted into channel 57 until it makes
contact with the surface 32. The thermocouple may then be glued or epoxied
in place. It is anticipated that this temperature information be utilized
in conjunction with known logic techniques to disable the laser diode
array upon reaching a maximum temperature. For example, the thermocouple
would indicate an over temperature condition of the microchannel cooler 30
should the channel 30 become clogged or coolant flow interrupted.
There has been described hereinabove a preferred exemplary embodiment of a
novel mounting module for a laser diode array. It is apparent that those
skilled in the art may now make numerous uses of and departures from the
above described embodiment without departing from the inventive concepts
disclosed herein. Accordingly, the present invention is to be defined
solely by the scope of the following claims.
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